1. Field of the Invention
The subject invention is generally directed to gerotor hydraulic devices that can be used as pumps and motors and, more specifically, to hydraulic balancing of moving parts in such devices.
2. Description of the Prior Art
Many types of prior art hydraulic devices have incorporated gerotor, or internal gear sets. Such devices have been used and described as both pumps and motors. Examples are shown in U.S. Pat. Nos. 3,572,983; 4,411,607; and 4,545,748. Briefly, an internal gear having outwardly directed teeth cooperates with either an external gear having inwardly directed teeth or, alternatively, an external ring that is maintained in an outer housing. The internal gear and external gear or ring defined fluid chambers. The internal gear and external gear or ring have a different number of teeth and are sized such that the fluid chambers expand and contract as the gears rotate. Thus, a basis for conversion between fluid pressure and mechanical torque is provided.
In such gerotor devices, as in other hydraulic devices, it is important that moving components be hydraulically balanced. Unbalanced components are subject to excessive friction and asymmetrical movement. Excessive friction accelerates mechanical wear and shortens the useful life of the device. Asymmetrical movement such as tilting, eccentricity, or skewing increases hydraulic leakage and friction which reduces mechanical efficiency and comprises the operating efficiency of the device.
As with other types of hydraulic devices, gerotor, or internal gear, pumps and motors require hydraulic balancing to achieve high efficiency and to realize their useful working life. To attain good performance, internal gear devices generally use a type of rotary face valve that employs lapped surfaces to effect tightly controlled clearances. However, the tight clearance of such rotary valves demands that the rotary valve be hydraulically balanced.
In the prior art, the rotary valve was usually balanced through the use of a fixed plate that separated the displacement element from the rotary valve. One example of such a fixed plate is shown and described in U.S. Pat. No. 3,572,983. In that patent, the hydraulic force generated by the chambers on one half of the displacement element is absorbed by one side of the fixed plate. The opposite side of the fixed plate absorbs the hydraulic forces developed by the high pressure ports of the rotary valve. Pressure areas are also provided on the valve side of the fixed plate to accomplish additional hydraulic balancing of the valve.
Other types of gerotor devices that employ a rotary valve have eliminated the need for a stationary plate. An example of a gerotor device having such a rotary valve is shown in U.S. Pat. No. 4,545,748. However, in rotary valve type gerotor devices without the fixed plate mentioned above, the rotary valve is subject to the hydraulic forces from both the displacement element chambers and the high pressure commutator ports. These forces place the rotary valve in a condition of hydraulic imbalance. Accordingly, compensation for the hydraulic forces acting on the rotary valve have been found to improve the efficiency and extend the operational life of the device.
A technique for partial balancing of the rotary valve in a gerotor device is shown in U.S. Pat. No. 4,411,607. In that patent, recessed sections and grooves are provided in the rotary valve face that is adjacent the commutator ports. The recessed sections and grooves are said to be arranged so that they develop a counterforce that opposes the force exerted on the rotary valve by the displacement element chambers. However, in the prior art, there was no mechanism for counterbalancing the force on the rotary valve from the high pressure commutator ports.
Accordingly, there was a need in the prior art for a mechanism to more completely hydraulically balance the rotary valves in gerotor devices. In addition, it was recognized that more complete balancing of other moving components in the gerotor device would further improve efficiency and performance.